Suitably pure freshwater is becoming increasingly valuable because of its scarcity, especially in populated areas where the general health of both people and livestock is influenced by the quality (or purity) of water used for drinking, cooking, washing, etc., and for agricultural irrigation where applicable. In 1986, the World Health Organization stated that an 80 percent decrease of illnesses would result if people in developing nations had access to pure drinking water (see Water 100% Natural, ©Rise L. Rafferty). The existence and continued production of poorly-sealed groundwater wells, such as those drilled by rotary methods, compounds the problem of groundwater purity in developed areas, by facilitating leakage to and from otherwise isolated groundwater veins. Many small islands in saltwater oceans are challenged to obtain sufficient freshwater economically, as current-technology desalination processes such as distillation and reverse osmosis tend to be capacity-limited, relative to their significant investment, maintenance cost, and service life limitations.
Collection of rainwater has long been a traditional source of low cost freshwater on a relatively small scale in non-arid locations, but in addition to being capacity-limited in most regions, the water quality produced by this method is influenced by air pollution, to the extent present in the surrounding atmosphere. The limitation of this source of supply to those time periods when weather patterns actually produce rain is what limits harvestable volumes to factors largely beyond the control of mankind.
Rain clouds are formed as moisture-laden air is elevated to altitudes of reduced atmospheric pressure, and cooled by this elevation and/or by movement of adjacent air masses, until the water vapor reaches a so-called saturation point, or dew point, where visible condensation, in the form of tiny aerosol droplets, begins to occur. Further cooling and/or pressure drops will increase the magnitude of condensation to the point of precipitation (rain) being formed by a process of droplet enlargement to sizes that allow gravitation to overcome air flow resistance, or so-called viscous effects. This typically occurs as a cold air mass or “cold front” meets warm air and, because of its greater density begins to flow under the warm air, both elevating and cooling it to produce the result of a transient period of rain.
Some geologic conditions, such as lakeshore bluffs or inland mountain ranges, act to produce clouds more or less continually as moisture-laden prevailing winds blow over and are elevated by them. A more or less constant threshold of cloud formation in these locations witnesses the fact of invisible water vapor in the moving air masses being both elevated to levels of lower atmospheric pressure, and cooled at these higher elevations, producing visible condensation such that freshly-formed clouds are consistently seen in proximity to the topographical features responsible for the elevation. The wind flows through the area of condensation, constantly regenerating cloud as the air rises and then dissipating it as the air descends on the other side of the landform or is warmed.
An example of such orographic conditions can be seen in the Caribbean island of St. Kitts, long known for its abundance of naturally-occurring mountain spring water. The prevailing Caribbean trade winds arrive after having traveled thousands of miles across the Atlantic Ocean, wherein “solar powered distillation” of ocean water occurs freely, and absent any significant sources of pollution, which tend to be land-based. These trade winds are deflected upward by the island's volcanic mountain range, which is providentially arrayed with respect to prevailing wind direction. The upwardly deflected flow reaches altitudes of over 2,000 feet ASL, where it tends to form clouds at the mountaintops. Numerous artesian wells on the sides of the mountains have traditionally supplied the towns and villages below with high quality water, and thus attest to the fact that these favorably created natural conditions are consistently near enough to the threshold of precipitation to enable the periodic rain from these clouds to be a reliable water source.
Such favorable orographic conditions offer, in the wind velocity and liquid water content of the clouds formed, copious quantities of freshwater for potentially energy-free harvest by an appropriately engineered precipitator-collector system. Such a “cloud catcher” water harvesting system offers the potential of producing voluminous quantities of freshwater directly from the clouds themselves (not being limited to the periodic precipitation associated with weather patterns), while being capable of also collecting naturally occurring precipitation, when it happens, as bonus water volume.
The practice of so-called fog collection in such localities is known, consisting of the placement of coarse mesh panels normal to wind direction, with collection troughs situated below the mesh panels to transport collected water to pipe manifolds leading to a reservoir. This technology has been shown to be effective in providing freshwater to small populations with very low investment cost, but suffers from the limitations of very low collection efficiency (counterproductive to spatial density, hence demanding of land area), and vulnerability to environmental (weathering, storm) damages so is poorly suited to reliably high volume production for areas of significant population density.
Accordingly, there exists a need for a more economical, durable, space-efficient production of voluminous quantities of freshwater than is provided by current technology, to benefit the many regions of the world where orographic cloud formations are in close enough proximity to user groups to enable cost-effective distribution of the new quantities of water thereby offered. Preferably, this would operate passively (without need for power sources), and with minimal operating and maintenance costs.
The technical challenges of collecting the liquid water of an orographic cloud or flowing fog lie firstly in the very small sizes of the droplet particles, and secondly in their low mixture density with the air that carries them. The sheer volume of flowing air mass, however, offers compensation for this relative rarity if reasonable collection efficiency can be achieved. A 10 m/s (22.37 mph) velocity orographic flow through a square window, 30 m (98.4 ft) per side can reasonably be estimated to pass water content on the order of 2334 m3/day (2.33 million liters/day), or 616,639 gallons/day.
With sizes on the order of 0.020 mm, the aerosol particles tend to flow around filtration media fibers rather than collide with them, as their viscous relationship with the air strongly prevails over the inertia effects required to move them across the streamlines of the air flow path. This, when coupled with their sparse population (with total liquid water content of a maritime stratus cloud on the order of 0.3 g/m3), makes particle impact with filtration media fibers quite low in frequency. Making the filtration media less coarse to increase fiber density is counterproductive to the extent that as flow resistance is increased, through-flow velocity is curtailed, making the (inertia-dependent) collisions with the fibers that much less probable.
A proven device for separating particles from air, which has been in use in industrial applications for over a century, uses centrifugal force to separate denser-than-air particles from a spiraling airflow path that is forced to spin within a cylindrical chamber. The so-called gas cyclone provides sufficient time for centrifugal force to migrate the bulk of condensate particles across the spinning air streamlines to the walls of the chamber where they collect and drain out at the bottom of the chamber.
These cyclone separators are passive, beyond the use of blowers or fans to produce sufficient airflow, in that no moving parts are required in their operation, but the pressure drop, or differential, between the inlet and the outlet required insure their successful operation is on the order of 100 mm of water, or 9.8 millibar (see A. C. Hoffmann & L. E. Stein; Gas Cyclones and Swirl Tubes; ISBN 3-540-43326-0, p. 312), much higher than the stagnation pressure of orographically-accelerated trade winds. Thus traditional-configuration cyclones are not suitable for the processing of voluminous quantities of cloud without the expenditure of inordinate amounts of power. In order to be passively powered by ambient air velocity directly, feasibility dictates that new, non-traditional configuration cyclones having very low pressure drop, on the order of 5% that of traditional devices, be proven effective in extracting liquid water from cloud aerosol. Such inventive cyclones are herein provided in conjunction with other preferred cloud catcher wind and water management structures, to enable substantially increased capture efficiency and productivity in comparison with traditional fog collection methodology. With design focus on volume of water collected, instead of dryness of output flow, these new non-traditional cyclones will not benefit the field of traditional-objective cyclones as configured in their entirety, although portions of the inventive structures may prove useful for alternative purposes.